1) I use one piece airlocks, they are they s shaped airlocks. You can fill them with water, sanitizer solution, or vodka. They last forever as long as they continue to seal properly and of course can be used more then once.
2) To use a hydrometer, you must remove a sample from your brew. You can siphon this out, use a wine thief, or just a turkey baster. You need to take it out with out adding oxygen to your brew, so never pour anything out of your brew. Your hydrometer should come with a testing tube, fill with mostly with your sample. Throw in the hydrometer and it will float. There are lines on the side of it representing the Specific gravity of your mixture. This is essentially how much sugar you have in solution. To find out how much alcohol you have, you need to take a reading prior to fermentation, before adding yeast, and after fermentation. starting SG - final SG divided by 7.5 is your abv %.
To find out when it is done fermenting, you should take several hydrometer readings, when you have 3 consistent readings over a week and they make sense, then it is done.
3) When it is done fermenting, completely. Mix 1 oz of priming sugar per gallon with just enough water to boil and dissolve it in. Throw this in your bottling bucket, or wherever you will be bottling from. Siphon your brew on top of this, the siphoning will be enough to properly mix the two together. Bottle it right away and it will carbonate in between 1 and 3 or so weeks. There is not normally any need to add yeast, as there is usually yeast still in solution.